Coal Seams

Other Regions. In AustraUa, Victoria has the largest reserves, although smaller ones occur in southern AustraUa, western AustraUa, Tasmania, and Queensland (28). The main deposit consists of many thick seams in about 500 km of the Latrobe Valley. The YaHourn coal field provides most of the fuel. The top coal seam is 65 m thick and is covered with 13 m of overburden. Most of this coal is used for electric power generation. It is very moist (55—72%), but has less than 5% ash. The lignitic coal found in South AustraUa is, for the most part, too deep for economic recovery. However, some of the better deposits are mined for power generation. 

A variety of measures must be taken to assure safe and continued operation. Because the natural water table is higher than the coal seams, or the seams are natural aquifers, it is necessary to pump water out of the pit or to drill weUs around the mine and pump to reduce the water table. The Rheinische Braunkohlenwerke (Rheinbraun) pumps water at a rate of 1-1.2 x 10 m /yr. Part of this water is processed to provide drinking water for Neuss and Dusseldorf. The tendency of lignite to ignite spontaneously requires care in the amount of face that is exposed, especially in naturally dry, hot, windy climates. 

Mineral Matter in Goal. The mineral matter (7,38) in coal results from several separate processes. Some comes from the material inherent in all living matter some from the detrital minerals deposited during the time of peat formation and a third type from secondary minerals that crystallized from water which has percolated through the coal seams. 

Coking coal is cleaned so that the coke ash content is not over 10%. An upper limit of 1—2 wt % sulfur is recommended for blast furnace coke. A high sulfur content causes steel (qv) to be brittle and difficult to roU. Some coal seams have coking properties suitable for metallurgical coke, but the high sulfur prevents that appHcation. Small amounts of phosphoms also make steel brittle, thus low phosphoms coals are needed for coke production, especially if the iron (qv) ore contains phosphoms. 

Another method used in Europe for steeply inclined seams is caked horizontal mining. Horizontal shafts are cut through rock below the coal seams. Vertical connections are then made to the seam to permit coal removal. 

Drainage. Some mines are located beneath subsurface streams, or the coal seams may be aquifers. These mines may become flooded if not continually pumped. In Peimsylvania anthracite mines as much as 30 tons of water maybe pumped for each ton of coal mined (94). 

In addition to carbon, all coals contains many noncombustible mineral impurities. The residue from these minerals after coal has been burned is called ash. Average ash content of the entire thickness of a coal seam typically ranges from 2 to 3 percent, even for very pure bituminous coals, and 10 percent or... 

A slope mine is one in which the coal is of moderate depth and where access is made through an inclined slope (maximum, 16°). This type of mining also may follow the coalbed if the coal seam itself is included and outcrops, or the slope may be driven in rock strata overlying the coal to reach the coal seam. Either a belt conveyor (no more than 30% grade), coal trucks (maximum grade, 18%), or electrical hoist if the slope is steep, can be used to transport coal out of the mine. 

When the coal seam is deep, a shaft mine is used because the other two types of access are cost-pro-... 

In addition to hydraulic fracturing, there are other stimulation techniques such as acid fracturing or matrix stimulation. Hydraulic fracturing finds use not only in the stimulation of oil and gas reservoirs, but also in coal seams to stimulate the flow of methane from there. 

Treating a coal seam with a well treatment fluid containing a dewatering agent will enhance methane production through a well. This additive enhances the permeability of the formation to water production and binds tenaciously to the coal surface so that the permeability-enhancement benefits are realized over a long production term. 

W. M. Harms and E. Scott. Method for stimulating methane production from coal seams. Patent US 5249627,1993. 

K. H. Nimerick and J. J. Hinkel. Enhanced methane production from coal seams by dewatering. Patent EP 444760,1991. 

At present, there are three possible geological structures that may be considered for C02 storage depleted hydrocarbon and production, deep saline aquifers, and coal seams. 

C02 in gaseous form is injected into the coalbed, 300 to 600 metre depth, and adsorbed on the matrix pores, releasing the existing CH4 in the same (two molecules of C02 adsorbed by each CH4 molecule that travels). This has led to the possibility of storing C02 in coal seams, while CH4 recovered is valued. This technique is called enhanced coalbed methane production (ECBM). 

PhungQ.H., Kyuro S., et al. Numerical simulation of C02 enhanced coal bed methane recovery for a Vietnamese coal seam. 2010 Journal of Novel Carbon Resource Science 2 1-7. 

Before mining commences, shafts are driven from the surface to the required depth. At least two shafts are required for ventilation to be possible. From these shafts, tunnels called stone drifts are made, roughly horizontally, to the coal seams. The seams may be 1 m or more thick and are usually inclined at an angle to the horizontal. 

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